Field of the Invention
This disclosure relates to an exhaust gas turbocharger for an internal combustion engine. More particularly, this disclosure relates to a heat shield for an exhaust gas turbocharger.
Description of Related Art
A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting the horsepower of the engine without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the exhaust manifold of the engine, a compressor housing connected to the intake manifold of the engine, and a center bearing housing disposed between and coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft is radially supported for rotation in the center bearing housing, and connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines a line which is the axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the cylinders of the engine via the engine intake manifold.
A heat shield is placed between the turbine wheel and the bearing housing. The heat shield is used to shield the bearing housing from the heat of the exhaust gases passing through the turbine housing and driving the turbine wheel. The heat shield includes a central opening that receives the shaft, whereby the heat shield is generally radially centered on the shaft relative to the bearing housing during assembly. However, the central opening is relatively large to permit thermal growth of the heat shield and shaft during operation of the turbocharger. As a result, the heat shield is often imprecisely positioned within the turbocharger during assembly with the bearing housing. When the turbine housing is subsequently assembled on the bearing housing during assembly of the turbocharger, the radial position of the heat shield cannot be determined since the turbine housing provides a visual obstruction, further exacerbating the difficulties in accurately positioning the heat shield within the overall assembly.